<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        [v-model]{
            width: 500px;;
        }
    </style>
</head>

<body>
    <div id="app">
        <input type="text" v-model="msg">
        <span>{{msg}}</span>
    </div>
    <script>
        /* new Vue({
            el:'',
            data:{
                msg:''
            }
        }) */

        export default{
            data:function(){
                return {
                    msg
                }
            }
        }
    </script>
</body>

</html>